Ionogels, formed by confinement of ionic conductive ionic liquids (ILs) within ionic conductive solid scaffolds (such as polymers or ceramics), show a unique combination of favorable properties which makes them stand out among all choices of solid electrolytes (SEs). Despite recent advances in enhancing the ionic conductivity of ionogel SEs, their electrochemical performance, including achievable C-rate and cycling stability, remains notably inferior to those of liquid electrolyte-based batteries, owning primarily to the obscure Li-ion transport mechanisms in the bulk, at intrinsic interphases, and at extrinsic interfaces with electrode. Furthermore, the unfavorable Li-ion molecular environment leads to lower mobility and higher ion-dissociation barriers, which contributes to the discontinuous ion-transport pathways within ionogel SEs and substantial resistance at the extrinsic electrode | electrolyte interface. In this study, we tuned the ionic conductivity and the ion-transport pathways of the polymer-encapsulated ionogels by changing the structure and mesh size of the polymeric network. Specifically, freestanding, soft ionogel SEs were prepared by UV-initiated photopolymerization based on thiol-ene reaction between thiol acrylate monomers and poly(ethylene glycol) diacrylate (PEGDA, average Mn=700 g/mol or 6000 g/mol) and poly(ethylene glycol) methyl ether methacrylate (PEGMA), in the presence of ionic liquid l-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide(EMIMTFSI) and lithium bis(trifluoromethane sulfonyl)imide(LiTFSI) salt. By varying the molar ratio of monomers during the thiol-ene reaction, three groups of samples with different mesh sizes (i.e. “low”, “medium”, and “high”) and different crosslinking structures were obtained. When the mesh size increases from “low” to “high”, the conductivity increases by nearly one order magnitude, reaching up to 2.07 x 10-3 S cm-1. In addition, when changing the IL loading amount from 25% to 75% at fixed mesh size and structure, the ionic conductivity increases significantly (9.45x10-6 S cm-1 to .07 x 10-3 S cm-1), indicating the dominant ion-transport medium in this binary ionogel is the IL phase. As a result of the synergistic effect of high bulk transport within IL phase and favorable intrinsic IL|Polymer interphase, the ionic conductivity of the ionogel SE reaches comparable with that of liquid electrolyte. Furthermore, the unreacted thiol groups in the terminal resulted in a reactive and sticky surface, which could improve the extrinsic interfacial contact between the ionogel SE and electrode materials.


We appreciate the funding support from URCA and FYSP programs of Kennesaw State University

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